Chlamydia pneumoniae is a human respiratory pathogen that causes 5 percent to 10 percent of pneumonia, bronchitis, and sinusitis. Virtually everyone is infected in his or her lifetime and reinfection is common. Infection is difficult to treat even with sensitive antibiotics. Chronic infection is common and has been associated with asthma, reactive airway disease, Reiter's syndrome, erythema nodosum, and sarcoidosis. The potential public health impact of infection with this pathogen is underscored by the association of C. pneumoniae with atherosclerosis and related clinical manifestations such as coronary heart disease, carotid artery stenosis, aortic aneurysm, claudication, and stroke. If C. pneumoniae infection plays a role in atherogenesis, there will be an urgent need to facilitate diagnosis and develop strategies for intervention and prevention. The overall goal of this proposal is two fold. First, C. pneumoniae specific antigens that are recognized during human infection will be exploited to facilitate serodiagnosis and identify putative vaccine candidates. The second goal is to define chlamydial/host cell interactions that lead to entry and survival of C. pneumoniae in host cells relevant to atherosclerosis. The specific focus will be on the interaction of the chlamydial glycan moiety with carbohydrate binding receptors on the host cell. Importantly, infection of epithelial cells can be inhibited with N-linked high mannose type oligosaccharide, the major component of the glycan. The novel hypothesis to be tested is that C. pneumoniae enters through the mannose-6 phosphate receptor by binding to the site involved in transport of phosphomannosylated residues to the lysosome and this differs from C. trachomatis, which utilizes the mannose receptor. The ultimate goals of these studies are to identify C. pneumoniae specific antigens to facilitate laboratory diagnosis and virulence factors playing a role in pathogenesis to guide vaccine development or develop anti-adhesive strategies for prevention of infection.